1. Field of the Invention
The present invention relates to a method of manufacturing a liquid crystal display device, and particularly, to a method of manufacturing a liquid crystal display device configured to hold a gap between substrates by a pillar spacer.
2. Description of the Background Art
In a general liquid crystal display device, a gap between a pair of opposing substrates is held constant by a spacer, and liquid crystal is filled between the substrates. Source lines and gate lines are arranged to cross each other in a matrix on one substrate, and a thin-film transistor is arranged on its intersection. Thus, this substrate is formed as an active matrix substrate (TFT substrate).
The other substrate is a filter substrate on which color filters (CF) are arranged, wherein a pixel portion is defined by a black matrix (hereinafter referred to as BM), and color filters of R (red), G (green), and B (blue) are formed on the pixel portion.
A transmissive or semi-transmissive liquid crystal display device includes a light source device such as a backlight. Here, the description of the light source device is skipped.
Examples of the spacer holding the gap between the substrates include particulate spacer beads, each having a diameter of about a few micrometers, and a pillar spacer provided by forming a pillar projection on a substrate.
However, spacer beads are randomly scattered on the substrate, so that they might be arranged even on a pixel portion. In this case, a light leakage is caused due to a disturbance in the alignment of the liquid crystal around the spacer beads, which entails a problem of deteriorating an image quality, such as a problem of reducing an image contrast. This is described in Japanese Patent Application Laid-Open No. 2005-258422.
In view of this, a liquid crystal display device requiring a satisfactory display quality tends to use a pillar spacer.
However, when the temperature of the liquid crystal display device using the pillar spacer increases, the elastic deformation of the pillar spacer cannot keep up with the thermal expansion of the liquid crystal, so that the liquid crystal stays on the lower side of the panel by a gravity force. This causes a gap unevenness (gravity unevenness, high-temperature gap unevenness, high-temperature swelling toward the bottom) in which the gap on the lower side of the panel increases. At low temperature, the elastic deformation of the pillar spacer cannot keep up with the thermal contraction of the liquid crystal, so that an internal pressure of the liquid crystal rapidly decreases to cause a low-temperature bubbling phenomenon in which air bubbles are generated, as described in Japanese Patent Application Laid-Open No. 2008-65077, for example.
For these problems, the above-mentioned Japanese Patent Application Laid-Open Nos. 2005-258422 and 2008-65077 describe a technique in which, as an initial design value, an elastic deformation ratio of a pillar spacer is specified and a height of the pillar spacer is measured, and an optimum amount of liquid crystal is determined according to the initial design value, and a technique of using a pillar spacer whose deformation range is large in order to increase a margin for the high-temperature gap unevenness and the low-temperature bubbling phenomenon. However, the variation in the height of the pillar spacer during the manufacture and the variation in the actual amount of the liquid crystal have to be considered. Therefore, a margin sufficient for covering the variation cannot actually be secured.
The defect such as the low-temperature bubbling phenomenon and high-temperature gap unevenness described above occurs during the use of the product after the shipment. These problems are involved with reliability of the product, and have to be eradicated.
Therefore, during a mass-production of actual products, a high-temperature test and low-temperature test are carried out for all of the actually manufactured liquid crystal display devices, as a finishing control, for confirming whether or not the high-temperature gap unevenness and low-temperature bubbling phenomenon occurs.
This leads to a long work period, and troublesome work, which increases cost. The use of the pillar spacer having large elastic deformation range for increasing the margin as described above might increase cost due to the development of the pillar spacer and increase in material cost. Since the elastic deformation is easy with the general substrate gap, the gap between the substrates cannot stably be held, resulting in that a new problem of an occurrence of non-uniform display caused by vibration might arise.